Adaptation of handover parameters

ABSTRACT

Handover parameter settings are automatically adapted in access points in a system to improve handover performance. Reactive detection techniques are employed for identifying different types of handover-related failures and adapting handover parameters based on this detection. Messaging schemes are also employed for providing handover-related information to access points. Proactive detection techniques also may be used for identifying conditions that may lead to handover-related failures and then adapting handover parameters in an attempt to prevent such handover-related failures. Ping-ponging may be mitigated by adapting handover parameters based on analysis of access terminal visited cell history acquired by access points in the system. In addition, configurable parameters (e.g., timer values) may be used to detect handover-related failures.

CLAIM OF PRIORITY

This application claims the benefit of and priority to commonly ownedU.S. Provisional Patent Application No. 61/142,862, filed Jan. 6, 2009,U.S. Provisional Patent Application No. 61/158,993, filed Mar. 10, 2009,U.S. Provisional Patent Application No. 61/160,218, filed Mar. 13, 2009,U.S. Provisional Patent Application No. 61/158,988, filed Mar. 10, 2009,and U.S. Provisional Patent Application No. 61/160,222, filed Mar. 13,2009, the disclosure of each of which is hereby incorporated byreference herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. 12/651,746, entitled “HANDOVER FAILUREMESSAGING SCHEMES,” the disclosure of which is hereby incorporated byreference herein.

BACKGROUND

1. Field

This application relates generally to communication and morespecifically, but not exclusively, to improving communicationperformance by adapting handover parameters.

2. Introduction

A wireless communication network is deployed over a defined geographicalarea to provide various types of services (e.g., voice, data, multimediaservices, etc.) to users within that geographical area. In a typicalimplementation, access points (e.g., corresponding to different cells)are distributed throughout a network to provide wireless connectivityfor access terminals (e.g., cell phones) that are operating within thegeographical area served by the network. In general, at a given point intime, the access terminal will be served by a given one of these accesspoints. As the access terminal roams throughout this geographical area,the access terminal may move away from its serving access point and movecloser to another access point. In addition, signal conditions within agiven cell may change, whereby an access terminal may be better servedby another access point. In these cases, to maintain mobility for theaccess terminal, the access terminal may be handed-over from its servingaccess point to the other access point.

Preferably, handover occurs without any loss or disruption to thecurrent communications path. In practice, however, various handoverfailures may occur. Such failures may include, for example, radio linkfailures (RLFs) and call drops. Some of these failures relate tohandover parameters that may be manually configured or improperlycontrolled. When these parameters are not optimally configured, handoverfailures can occur. These failures may generally fall in to four maincategories: 1) handovers that occur too early; 2) handovers that occurtoo late; 3) handovers that are not triggered properly; and 4) handoversthat bounce back and forth between access points (which is sometimesreferred to as “ping-ponging”).

SUMMARY

A summary of sample aspects of the disclosure follows. In the discussionherein, any reference to the term aspects may refer to one or moreaspects of the disclosure.

The disclosure relates in some aspects to handover parameter adaptation(e.g., optimization). In some aspects of the disclosure, differentschemes are disclosed for facilitating a self-optimization function ataccess points in a system. Here, handover parameter settings areautomatically adapted by the access points (e.g., without humanintervention) to improve (e.g., maximize) handover performance in thesystem. For example, an access point may automatically detect incorrector sub-optimal handover parameter settings by detecting handover-relatedfailures and unnecessary handovers (e.g., ping-ponging). The accesspoint may then adapt the handover parameter settings to reduce thenumber of handover-related failures and reduce inefficient use ofnetwork resources due to unnecessary handovers. In this way, degradationin user experience (e.g., call drops, RLFs, reduced data rates, andinefficient network resource utilization) caused by improper handoverparameter settings may be reduced. Examples of handover parameters thatmay be adapted include time-to-trigger (TTT) parameters, offsetparameters, and Cell Individual Offsets (CIO).

The disclosure relates in some aspects to reactive detection techniquesfor identifying different types of handover-related failures andadapting handover parameters based on this detection. For example, anaccess point may detect a handover-related failure that occurred as aresult of a handover being performed too late and then adapt one or morehandover parameters in an attempt to prevent such too late handovers. Asanother example, an access point may detect RLF that occurred as aresult of a handover not being performed and then adapt one or morehandover parameters in an attempt to prevent such RLFs. In addition, anaccess point may detect a handover-related failure that occurred as aresult of a handover being performed too early and then adapt one ormore handover parameters in an attempt to prevent such too earlyhandovers. Also, an access point may detect a handover-related failurethat occurred as a result of an access terminal being handed-over to thewrong cell and then adapt one or more handover parameters in an attemptto prevent such handovers to the wrong cell.

The disclosure relates in some aspects to messaging schemes forproviding handover-related information to access points. For example, ifan access point detects RLF that occurred at another access point, theaccess point may send an RLF report message to that other access point.In this way, the other access point may determine that its handoverparameters need to be adjusted based on the RLF report. As anotherexample, if an access point detects a failure (e.g., too early handoveror a handover to a wrong cell) for a handover that originated at anotheraccess point, the access point may send a handover report message tothat other access point. In this case, the other access point maydetermine that its handover parameters need to be adjusted based on thehandover report.

The disclosure relates in some aspects to proactive detection techniquesfor identifying conditions that may lead to handover-related failuresand then adapting handover parameters in an attempt to prevent suchhandover-related failures. For example, an access point may monitor therelative signal strengths (of itself and surrounding access points) asreported by one or more access terminals and determine, based on thesesignal strengths, whether too late handovers or too early handovers arelikely to occur. If so, the access point may adjust one or more handoverparameters to mitigate too late handovers or too early handovers.

The disclosure relates in some aspects to reducing ping-ponging byadapting handover parameters based on analysis of visited cell historymaintained by access terminals in the system. For example, an accessterminal may send its visited cell history to an access point when theaccess terminal is handed-over to that access point. The access pointmay then detect ping-ponging by analyzing the visited cell history(e.g., identifying the visited cells and the time spent at each cell).Upon detection of ping-ponging, the access point may adapt one or morehandover parameters to reduce the likelihood of such ping-ponging in thefuture.

The disclosure relates in some aspects to configuring parameters (e.g.,timer values) that are used to detect handover-related failures. Forexample, a network management system may configure parameters for accesspoints in a system and send these parameters to the access points. Theaccess points may then use the parameters to detect handover-relatedfailures such as too early handovers and handovers to the wrong cell.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the appended claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified block diagram of several sample aspects of acommunication system adapted to provide handover parameter optimization;

FIG. 2 is a simplified block diagram of several sample aspects of acommunication system adapted to detect a too late handover failure and,in response, adapt handover parameters to mitigate too late handoverfailures;

FIG. 3 is a simplified block diagram of several sample aspects of acommunication system adapted to detect a too early handover failure and,in response, adapt handover parameters to mitigate too early handoverfailures;

FIG. 4 is a simplified block diagram of several sample aspects of acommunication system adapted to detect handover to the wrong cell and,in response, adapt handover parameters to mitigate handovers to thewrong cell;

FIG. 5 is a flowchart of several sample aspects of operations that maybe performed to detect a first type of too late handover (e.g., afailure to handover) and, in response, adapt handover parameters tomitigate too late handover failures;

FIG. 6 is a flowchart of several sample aspects of operations that maybe performed to detect a second type of too late handover failure and,in response, adapt handover parameters to mitigate too late handoverfailures;

FIG. 7 is a flowchart of several sample aspects of operations that maybe performed to detect a first type of too early handover failure and,in response, adapt handover parameters to mitigate too early handoverfailures;

FIG. 8 is a flowchart of several sample aspects of operations that maybe performed to detect a first type of too early handover failure and,in response, adapt handover parameters to mitigate too early handoverfailures;

FIGS. 9A and 9B are a flowchart of several sample aspects of operationsthat may be performed to detect a second type of too early handoverfailure and, in response, adapt handover parameters to mitigatehandovers to the wrong cell;

FIG. 10 is a flowchart of several sample aspects of additionaloperations that may be performed to detect a first type of handover tothe wrong cell and, in response, adapt handover parameters to mitigatehandovers to the wrong cell;

FIGS. 11A and 11B are a flowchart of several sample aspects ofoperations that may be performed to detect a second type of handover tothe wrong cell and, in response, adapt handover parameters to mitigatehandovers to the wrong cell;

FIG. 12 is a flowchart of several sample aspects of operations that maybe performed to proactively detect handover-related failures;

FIGS. 13A and 13B are simplified diagrams illustrating indications ofsignal quality that may be used to proactively detect handover-relatedfailures;

FIG. 14 is a flowchart of several sample aspects of operations that maybe performed to mitigate ping-ponging;

FIG. 15 is a flowchart of several sample aspects of operations that maybe performed to configure handover-related parameters;

FIG. 16 is a flowchart of several sample aspects of operations that maybe performed to handle intra-access point and inter-access pointhandover-related failures;

FIG. 17 is a flowchart of several sample aspects of operations that maybe performed to handle inter-access point handover-related failures;

FIG. 18 is a simplified block diagram of several sample aspects ofcomponents that may be employed in communication nodes;

FIG. 19 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 20-26 are simplified block diagrams of several sample aspects ofapparatuses that may be employed in conjunction with providing handoverparameter adaptation as taught herein.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatus(e.g., device) or method. Finally, like reference numerals may be usedto denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim.

FIG. 1 illustrates several nodes of a sample communication system 100(e.g., a portion of a communication network). For illustration purposes,various aspects of the disclosure will be described in the context ofone or more access terminals, access points, and network nodes thatcommunicate with one another. It should be appreciated, however, thatthe teachings herein may be applicable to other types of apparatuses orother similar apparatuses that are referenced using other terminology.For example, in various implementations access points may be referred toor implemented as base stations, eNodeBs, cells, and so on, while accessterminals may be referred to or implemented as user equipment, mobiles,and so on.

Access points in the system 100 provide one or more services (e.g.,network connectivity) for one or more wireless terminals (e.g., accessterminal 102) that may be installed within or that may roam throughout acoverage area of the system 100. For example, at various points in timethe access terminal 102 may connect to an access point 104, an accesspoint 106, or an access point 108. Each of the access points 104-108 maycommunicate with one or more network nodes (represented, forconvenience, by network node 110) to facilitate wide area networkconnectivity. These network nodes may take various forms such as, forexample, one or more radio and/or core network entities. Thus, invarious implementations the network node 110 may represent functionalitysuch as at least one of: network management (e.g., via an operation,administration, management, and provisioning entity), call control,session management, mobility management, gateway functions, interworkingfunctions, or some other suitable network functionality.

In accordance with the teachings herein, the access points 104, 106, and108 include handover parameter optimization components 112, 114, and116, respectively, to provide self-optimization of one or moreparameters used by the access points during handover operations. Thesehandover parameters may include, for example, a time-to-trigger (TTT)parameter, an offset for a serving cell, a Cell Individual Offset (CIO),a hysteresis parameter for an event, and a cell re-selection parameter.

To provide self-optimization of such handover parameters, the accesspoints may detect certain types of handover-related problems and thenadapt one or more handover parameters in an appropriate manner in anattempt to prevent those types of handover-related problems fromoccurring in the future. For example, handover failures may occur as aresult of too early handover triggering, too late handover triggering,handovers not being triggered, and handovers to the wrong cell. Here,handovers that are not triggered due to RLF occurring prior to handovertriggering may be considered as a subset of too late handovertriggering. In addition, system performance may be adversely affected ifan access terminal is successively handed-over between access points (orcells) where the access terminal connects to each access point for onlya relatively short period of time (ping-ponging). Thus, in some aspects,the description that follows relates to reducing the occurrences of toolate handovers, too early handovers, handovers to the wrong cell, andping-ponging.

To facilitate detection of these handover-related problems, the accesspoints may receive handover-related messages (e.g., as indicated by thedashed lines in FIG. 1) from other nodes in the system 100. As discussedin more detail below, these messages may comprise, for example, handoverfailure-related messages such as RLF report messages (e.g., RLFindication messages or RLF event reports) and handover report messages(e.g., handover event reports), and ping-ponging information messagessuch as messages including access terminal history information. Uponreceiving one of these handover-related messages, an access point mayidentify one of these above types of handover-related problems and thenadapt an appropriate handover parameter in an attempt to mitigate thisparticular type of handover problem.

In some cases, an access point will use one or more parameters fordetecting a handover-related failure. For example, an access point mayemploy a timer to determine whether an RLF occurred within a definedperiod of time after an access terminal was handed-over. To facilitateeffective detection of such events, a network management system 118 mayconfigure these parameters and then send these parameters to the accesspoints in the system 100.

With the above overview in mind, various techniques that may be employedto adapt handover parameters in accordance with the teachings hereinwill be described with reference to FIGS. 2-17. For illustrationpurposes, the operations of the flowcharts of FIGS. 5-12 and 14-17 (orany other operations discussed or taught herein) may be described asbeing performed by specific components (e.g., components shown in FIGS.1-4 or FIG. 18). It should be appreciated, however, that theseoperations may be performed by other types of components and may beperformed using a different number of components. It also should beappreciated that one or more of the operations described herein may notbe employed in a given implementation.

FIGS. 2-4 illustrate messaging that may be employed to detect ahandover-related failure. FIG. 2 illustrates messaging that may beemployed to facilitate detection of a too late handover. FIG. 3illustrates messaging that may be employed to facilitate detection of atoo early handover. FIG. 4 illustrates messaging that may be employed tofacilitate detection of a handover to the wrong cell.

Referring initially to the detection of too late handovers, if accessterminal mobility is more aggressive than what the handover parametersettings allow for, handover may be triggered when the signal strengthof the source is already too low—leading to RLF. Moreover, handover maynot be triggered at all if an RLF preempts handover. These scenarios maybe common in areas with high user mobility (e.g., along a highway, on ahigh speed train, etc.)

In FIG. 2, an access terminal 202 is in the vicinity of an access point204 and an access point 206. Initially, the access terminal 202 isconnected to the access point 204 (e.g., a cell of the access point204). Here, RLF may occur as a result of inadequate configuration ofhandover triggering parameters at the access point 204 (e.g., asdiscussed above). In the event the signal quality provided by the accesspoint 206 is sufficient to maintain a call for the access terminal 202,the access terminal 202 may re-establish the connection at the accesspoint 206 (e.g., at a cell of the access point 206).

In one sample implementation, there are two types of too late handovers.In a first type of too late handover, RLF occurs before the access point204 receives a handover-triggering measurement report message from theaccess terminal 202. Thus, in this case, RLF occurs before any handoveroperations have commenced. In a second type of too late handover, RLFoccurs after the access point 204 receives a handover-triggeringmeasurement report message from the access terminal 202, but before theaccess terminal 202 receives a handover command from the access point204. Thus, in this case, the access point 204 has commenced handoveroperations, however, RLF occurs before the handover operations arecompleted.

Referring initially to the first type of too late handover, if theaccess terminal 202 re-establishes the connection at the access point206 after RLF at the access point 204, the access point 206 reports thisRLF event to the access point 204 via an RLF report message (asrepresented by the dashed line in FIG. 2). In other words, if the accessterminal 202 re-establishes (or attempts to re-establish) the radio linkat the access point 206 after RLF at the access point 204, the accesspoint 206 reports this RLF event to the access point 204. Here, theaccess point 206 may use an identifier (e.g., physical cell identifier,PCI) provided by the access terminal during connection re-establishmentto identify the previous serving cell/access point (or possiblecandidates in the case of identifier confusion) for the access terminal.The access point 204 may then detect a too late handover based on thisRLF report message. For example, the access point 204 may match thecorrect context (based on an access terminal identifier included in theRLF report message), and analyze the possible root cause of the RLFwhich preceded the re-establishment request.

The above operations are represented by corresponding functional blocksin FIG. 2. Here, a component 208 of the access point 206 detects there-establishment of the connection by the access terminal 202 due toRLF. As a result of this connection re-establishment, a report generator210 sends the RLF report message to the access point 204. Upon receivingthis message, a too late detector 212 determines that the accessterminal 202 was not handed-over to the access point 206 soon enough.That is, a too late handover is detected. Consequently, a handoverparameter adapter 214 may adapt one or more handover parameters based onthe detection of the too late handover. As will be discussed in moredetail below, the adaptation of handover parameters may be based on thedetection of one or more too late handovers (e.g., associated with thesame cell or access point or different cells or access points).

The RLF report message may include various types of information toenable the access point 204 to determine that the access terminal 202was not handed-over soon enough to the access point 206. For example,the RLF report may include at least one of: an identifier of the accessterminal, an identifier of the cell and/or an identifier of the accesspoint at which the RLF occurred, an identifier of the cell and/or anidentifier of the access point at which the access terminal attemptedconnection re-establishment, a geographical location of the RLF, thetime when the RLF occurred, the type of the report (e.g., too latehandover), a frequency band on which the RLF occurred, a frequency bandon which the access terminal reconnected, or other information ofinterest for handover parameter optimization. The above identifiers maycomprise, for example, physical cell identifiers (PCIs), cell globalidentifiers (CGIs), MAC identifiers (e.g., a short MAC address), RNTIsfor the access terminal, or some other suitable identifier(s).

RLF events may be reported in various ways. In some implementations RLFevents are reported using event-based reporting. For example, an RLFevent may be reported each time an RLF event occurs. In someimplementations RLF events are reported periodically. Here, thereporting interval may be configurable (e.g., by a network managementsystem). In some implementations RLF events are reported usingrequest-based reporting (e.g., polling). For example, an access pointmay send an RLF report in response to a request from another accesspoint. In some implementations RLF events are reported usingpolicy-based event reporting. For example, RLF events may be reportedbased on configurable policy provided by a network operator (e.g., viaan operations and management (OAM) system).

In the example of FIG. 2, the RLF report is sent between access points(i.e., externally to an access point). Here, the RLF report may be sentover external access point interfaces using standardized protocols. Forexample, in an LTE-based system, the report may be sent over an X2interface using X2-AP protocol (specified in 3GPP TS 36.423) and/or overan S1 interface using S1-AP protocol (specified in 3GPP TS 36.413).

In other cases, a cell sending an RLF event report and a cell to whichthe RLF event report is sent may be parented by the same access point.In these cases, the RLF event report may be sent internally to an accesspoint (e.g., by operation of internal software of the access point).

Referring now to the second type of too late handover, in the course ofregular connected mode measurements while at the access point 204, theaccess terminal 202 detects a candidate access point (access point 206)that fulfills the criteria for sending a measurement report message(e.g., requesting handover). In this case, the access terminal 202successfully sends a measurement report message to the access point 204.The access point 204 then executes a handover preparation procedure(e.g., pursuant to TS 36.413 and 36.423 in an LTE-based system). Thus,the access point 204 attempts to send a handover command to the accessterminal 202 requesting handover to the access point 206. However, theaccess terminal 202 experiences RLF at the access point 204 before it isable to receive the handover command or before it is able tosuccessfully act on the handover command (e.g., connect to the accesspoint 206).

In this case, the access point 204 may autonomously detect the too latehandover and/or the access point 204 may detect the too late handoverbased on an RLF report message received from the access point 206 (e.g.,in a similar manner as described above for type 1 too late handoverdetection). In the former case, an RLF detector component 216 may detectthe RLF by the access terminal 202. For example, the access point 204may determine that the RLF occurred while the access point 204 wasattempting to transmit the handover command to the access terminal 202.In some aspects, the access point 204 may detect the RLF based on lossof lower-level synchronization with the access terminal 202.

Referring now to FIG. 3, sample messaging that may be employed inconjunction with detection of too early handovers will be described. Insome aspects, a too early handover may be triggered when the accessterminal enters an unintended island of coverage of another cellcontained inside the coverage area of a serving cell. This is a typicalscenario for areas where fragmented cell coverage is inherent to theradio propagation environment, such as in dense urban areas. A signatureof the too early handover is RLF in the target cell during handoverfollowed by connection re-establishment in the source cell.

In FIG. 3, an access terminal 302 is the vicinity of an access point 304and an access point 306 as above. The access terminal 302 is initiallyconnected to the access point 304 (e.g., a cell of the access point 304)and is then handed-over to the access point 306 (e.g., a cell of theaccess point 306). However, RLF occurs at the access point 306 duringhandover or soon after handover is completed as a result of inadequateconfiguration of handover triggering parameters at the access point 304.That is, due to these incorrect handover parameter settings, the accessterminal 302 was handed-over to the access point 306 too soon (e.g.,before the adequacy of the signal quality provided by the access point306 for the access terminal 302 could be established). As a result ofthis RLF, the access terminal 302 re-establishes the connection at theaccess point 304 (e.g., at a cell of the access point 304).

In one sample implementation, there are two types of too earlyhandovers. In a first type of too early handover, RLF occurs before theaccess terminal 302 successfully connects (e.g., transmits a handoverconfirm message) to the access point 306. In a second type of too latehandover, RLF occurs a short time after the access terminal 302successfully connects to the access point 306.

The access point 304 may autonomously detect the first type of too earlyhandover. These operations are represented by corresponding functionalblocks in FIG. 3. Here, a component 308 of the access point 304 detectsthe re-establishment of the connection by the access terminal 302 due toRLF. As a result of this connection re-establishment, a too earlydetector 310 determines that the access terminal 302 was handed-over tothe access point 306 too soon. That is, a too early handover isdetected. Consequently, a handover parameter adapter 312 may adapt oneor more handover parameters based on the detection of the too earlyhandover. As will be discussed in more detail below, the adaptation ofhandover parameters may be based on the detection of one or more tooearly handovers (e.g., associated with the same cell or access point ordifferent cells or access points).

Referring now to the second type of too early handover, the sourceand/or the target for the handover may employ a timer to detect thistype of too early handover. For example, the source may detect a tooearly handover based on whether an access terminal that was handed-overre-establishes a connection at the source within a defined period oftime after the handover was completed. Similarly, the target may detecta too early handover based on whether an RLF report concerning theaccess terminal's RLF at the target is received at the target within adefined period of time after the handover was completed. These detectionmechanisms will be discussed in turn with reference to FIG. 3.

The access point 304 may start a timer 314 (t_(early) _(—) _(HO) _(—)_(source)) when the access point 304 is informed that the handover fromthe access point 304 to the access point 306 was completed. For example,completion of the handover may be indicated when the access point 304receives a user equipment (UE) context release message from the accesspoint 306. If the access terminal 302 re-establishes the connection atthe access point 304 after RLF at the access point 306 before the timer314 expires, the too early detector 310 detects a too early handover.The handover parameter adapter 312 may then adapt one or more handoverparameters based on the detection of the too early handover.

In some cases, the source may elect to not report the RLF event to thetarget. However, in other cases (e.g., in implementations where thesource does not employ a timer and/or has deleted the UE context as aresult of the UE context release message), the source may send an RLFreport message to the target since the RLF event may appear to thesource to be a too late handover event for the target.

In this case, with reference to FIG. 3, the access point 306 may start atimer 316 (t_(early) _(—) _(HO) _(—) _(target)) when an incominghandover from the access point 304 is completed. For example, completionof the handover may be indicated by the access point 306 sending a UEcontext release message to the access point 304. If an RLF report isreceived from the access point 304 for the access terminal 302 beforethe timer 316 expires, the access point 306 determines that this reportindicates that the access terminal 302 was handed-over by the accesspoint 304 too early. In other words, the access point 306 determinesthat this report is not indicative of a too late handover by the accesspoint 306. Consequently, the access point 306 may not act on the RLFreport, a report generator 318 of the access point 306 may send ahandover report message to the access point 304 to inform the accesspoint 304 of the too early handover, or both actions may be taken.

Thus, the access point 306 may return an indication of a too earlyhandover event to the access point 304 when the access point 306receives an RLF report from the access point 304 and if the access point306 has sent the UE context release message to the access point 304related to the completion of an incoming handover for the same accessterminal within the defined period of time (t_(early) _(—) _(HO) _(—)_(target)). Upon receiving this message, the too early detector 310determines that the access terminal 302 was handed-over to the accesspoint 306 too soon. That is, a too early handover is detected.Consequently, the handover parameter adapter 312 may adapt one or morehandover parameters based on the detection of the too early handover.

The handover report message may include various types of information toenable the access point 304 to determine that the access terminal 302was handed-over to the access point 306 too early. For example, thehandover report may include at least one of: an identifier of the accessterminal, an identifier of the target (e.g., an identifier of the celland/or an identifier of the access point at which the RLF occurred), anidentifier of the source (e.g., an identifier of the cell and/or anidentifier of the access point at which the access terminal attemptedconnection re-establishment), the type of detected handover problem(e.g., too early handover), a handover cause (e.g., signaled by thesource during handover preparation), or other information of interestfor handover parameter optimization. The above identifiers may comprise,for example, physical cell identifiers (PCIs), cell global identifiers(CGIs), MAC identifiers (e.g., a short MAC address), RNTIs for theaccess terminal, or some other suitable identifier(s).

Handover reports may be reported in various ways. In someimplementations handover reports are reported using event-basedreporting. For example, a handover report may be reported each time acorresponding event occurs. In some implementations handover reports arereported periodically. Here, the reporting interval may be configurable(e.g., by a network management system). In some implementations handoverreports are reported using request-based reporting (e.g., polling). Forexample, an access point may send a handover report in response to arequest from other access point. In some implementations handoverreports are reported using policy-based event reporting. For example, ahandover report may be reported based on configurable policy provided bya network operator (e.g., via an operations and management (OAM)system).

In the example of FIG. 3, the handover report is sent between accesspoints (i.e., externally to an access point). Here, the handover reportmay be sent over external access point interfaces using standardizedprotocols. For example, in an LTE-based system, the report may be sentover an X2 interface using X2-AP protocol (specified in 3GPP TS 36.423)and/or over an S1 interface using S1-AP protocol (specified in 3GPP TS36.413).

In other cases, a cell sending a handover report and a cell to which thehandover report is sent may be parented by the same access point. Inthese cases, the handover report may be sent internally to an accesspoint (e.g., by operation of internal software of the access point).

Referring now to FIG. 4, sample messaging that may be employed inconjunction with detection of handovers to the wrong cell will bedescribed. In some aspects, handovers may be directed towards a wrongcell if handover parameters are set incorrectly. An example of asignature of a handover to a wrong cell is an RLF during handoverfollowed by connection re-establishment in a cell other than the sourcecell or the target cell. For purposes of illustration, the followingdiscussion will describe handover between cells. It should beappreciated, however, that the disclosed concepts are applicable tohandover between access points as well.

In one sample implementation, there are two types of handovers to thewrong cell. In a first type of handover to the wrong cell, RLF occurs inthe source cell before the access terminal successfully connects (e.g.,transmits a handover confirm message) to the target cell. In a secondtype of handover to the wrong cell, RLF occurs a short time after theaccess terminal successfully connects to the target cell.

Referring initially to the first type of handover, with reference toFIG. 4, at some point in time the handover of an access terminal 402 hasbeen initiated from a source cell (e.g. access point 404). For example,the access terminal 402 may have received a handover command messagefrom the source cell. However, RLF occurs at the source cell before theaccess terminal 402 is able to connect to the target cell (e.g. accesspoint 406). In some implementations, connection refers to successfultransmission of a handover confirm message. As a result of the RLF, theaccess terminal 402 re-establishes the connection at a third cell (e.g.access point 408) that is not the source cell or the target cell.

Upon detecting the re-establishment of the connection by the accessterminal 402 due to RLF (e.g., by a component 410 of the access point408), the third cell sends an RLF report message (e.g., as discussedherein) to the source cell. Upon receiving this message, the source cell(e.g., a wrong cell detector 412) determines that the access terminal402 was handed-over to the wrong cell (e.g., the access terminal 402 washanded-over to a cell that provided lower signal quality than the thirdcell). That is, a handover to the wrong cell is detected. Consequently,a handover parameter adapter 414 may adapt one or more handoverparameters based on the detection of the handover to the wrong cell. Asdiscussed herein, the adaptation of handover parameters may be based onthe detection of one or more handovers to the wrong cell (e.g.,associated with the same cell or access point or different cells oraccess points).

Referring now to the second type of handover to the wrong cell, thetarget may detect a handover to the wrong cell based on whether an RLFreport concerning the access terminal's RLF at the target is received atthe target within a defined period of time after the handover wascompleted. In some aspects, a signature of a handover to the wrong cellmay involve: 1) handover has been initiated from the source cell; 2) theaccess terminal connected to the target cell; 3) RLF occurred in thetarget cell; and 4) the access terminal reconnected in a third cell thatis not the source cell or the target cell.

Referring to FIG. 4, the target cell may start a timer 416 (t_(store)_(—) _(UE) _(—) _(context)) when an incoming handover from the accesspoint 404 is completed. For example, completion of the handover may beindicated by the access point 406 sending a UE context release messageto the access point 404. If the target cell receives an RLF report forthe access terminal 402 before the timer 416 pertaining to that accessterminal expires, the target cell will take appropriate action dependingupon which cell sent the RLF report. If the RLF report was received fromthe source cell (e.g., from the access point 404) the target cell mayelect to not act upon the RLF report as discussed herein. If, on theother hand, the RLF report was received from a cell (e.g., from theaccess point 408) other than the source cell, the target cell (e.g., areport generator 418) may send a handover report message (e.g., asdescribed herein) to the source cell to inform the source cell of thehandover to the wrong cell.

Thus, in this latter case, the target cell (e.g., access point 406) maysend a handover report message indicating a handover to a wrong cellevent to the source cell (e.g., access point 404) when the target cellreceives an RLF indication from the third cell (e.g., access point 408),and if the target cell has sent the UE context release message to thesource cell related to the completion of an incoming handover for thesame access terminal within a defined period of time (e.g., t_(store)_(—) _(UE) _(—) _(context) seconds).

Upon receiving this message, the wrong cell detector 412 determines thatthe access terminal 402 was handed-over to the wrong cell. That is,handover to the wrong cell is detected. Consequently, the handoverparameter adapter 414 may adapt one or more handover parameters based onthe detection of the handover to the wrong cell.

The handover report message may include similar information as discussedabove. In this case, however, the type of detected handover problem thatis indicated by the report will be a handover the wrong cell. Inaddition, the report may include an identifier of the wrong target(e.g., an identifier of the cell and/or an identifier of the accesspoint at which the RLF occurred), an identifier of a correct target(e.g., an identifier of the cell and/or an identifier of the accesspoint at which the access terminal attempted connectionre-establishment), and an identifier of the source (e.g., an identifierof the cell and/or an identifier of the access point that initiated thehandover).

FIGS. 5-11B describe sample operations (e.g., algorithms) that may beemployed for reactive detection. In some aspects, reactive detection isaimed at preventing future occurrences from happening based on receivedreports and analysis of past occurrences. For purposes of illustration,the following describes operations of cells and messaging between cells.It should be appreciated that these operations also may correspondgenerally to operations of access points and messaging between accesspoints.

The flowcharts of FIGS. 5 and 6 describe operations that may be employedto provide handover parameter adaptation based on detection of too latehandover. Specifically, FIG. 5 relates to the first type of too latehandover as discussed herein and FIG. 6 relates to the second type oftoo late handover as discussed herein.

As represented by block 502 of FIG. 5, at some point in time an accessterminal connects to a first cell (e.g., a first access point). Whileconnected to the first cell, the access terminal may detect a candidatecell (a second cell) that fulfills the criteria for sending ameasurement report message to the first cell. Consequently, the accessterminal may attempt to send a measurement report message to the firstcell.

As represented by block 504, however, the access terminal experiencesRLF at the first cell while attempting to send (or prior to sending) themeasurement report message. As discussed herein, the RLF may haveoccurred as a result of inadequate configuration of handover triggeringparameters at the first cell (e.g., first access point) that caused theaccess terminal to not be handed-over.

As represented by block 506, the access terminal re-establishes theconnection at the second cell. Here, the access terminal selects theaccess point of the second cell for re-establishing the connection afterthe RLF (e.g., based on received signal strengths of access pointsdetected by the access terminal). As discussed herein, in conjunctionwith the re-establishment of the connection, the second cell (e.g.,second access point) receives a message from the access terminal thatindicates that the access terminal experienced RLF at the first cell(e.g., a first access point). Here, the message identifies the cell(and/or access point) at which the RLF occurred.

As represented by block 508, the second cell (e.g., second access point)sends an RLF report message for this access terminal to the first cell.In some aspects, this message informs the first cell (e.g., first accesspoint) of the connection re-establishment. As discussed herein, thismessage may comprise, for example, an identifier of a cell at which theRLF occurred, an identifier of a cell at which the connection wasre-established, and an identifier of the access terminal. Also asdiscussed above, this report message may be sent according toevent-based, periodic, request based, policy-based reporting, or someother suitable reporting scheme. The first cell receives this reportmessage as represented by block 510.

As represented by block 512, the first cell detects too late handoverfailure based on the received RLF report message. For example, the firstcell may analyze the information in the report and conclude that thisrelates to the case of a too late handover from the first cell to thesecond cell. Thus, in some aspects, the detection of block 512 maycomprise detecting RLF due to too late handover. In some aspects, thedetection may comprise determining at a first cell (or access point)that RLF occurred prior to handover of the access terminal from thefirst cell to a second cell (or access point). In some aspects, thedetection may comprise receiving a message from a second cell (or accesspoint) at a first cell (or access point), wherein the message indicatesthat an access terminal re-establishing a connection at the second cellexperienced RLF at the first cell, and determining that the accessterminal was not handed-over to the second cell soon enough based on thereceived message.

As represented by block 514, the first cell adapts one or more handoverparameters based on the detection of too late handover failure. Forexample, the first cell may take the received information intoconsideration for the purpose of optimization of handover parameters toavoid too late handovers to the second cell in the future.

The adaptation of handover parameters as taught herein may take intoaccount one or more handover failure events. For example, a handoverparameter may be adapted for a specific cell based on detected too latehandovers associated with that cell and/or some other cell(s).Alternatively, a handover parameter may be adapted for a set of cellsbased on detected too late handovers failures associated with thosecells and/or some other cell(s).

Various types of handover parameters may be adapted here. For example,at least one of: a time-to-trigger (TTT) parameter, an offset for aserving cell, a Cell Individual Offset (CIO), or a hysteresis parameterfor an event, may be adapted (e.g., reduced) to reduce the likelihoodthat too late handovers will occur in the future.

Referring to the type 2 too late handover of FIG. 6, while connected tothe first cell, the access terminal may detect a candidate cell (asecond cell) that fulfills the criteria for sending a measurement reportmessage to the first cell. In this case, the access terminalsuccessfully sends the measurement report message to the first cell.Accordingly, handover of the access terminal to the second cell may becommenced as represented by block 602. Here, the first cell attempts tosend a handover command to the access terminal requesting handover tothe second cell.

As represented by block 604, however, the access terminal experiencesRLF at the second cell before the access terminal is able to receive thehandover command or before the access terminal is able to successfullyact on the handover command (e.g., successfully connect to the secondcell). As discussed herein, the RLF may have occurred as a result ofinadequate configuration of handover triggering parameters at the firstcell (e.g., first access point) that caused the handover from the firstcell (e.g., first access point) to the second cell (e.g., second accesspoint) to be triggered too late for successful handover.

As represented by block 606, the first cell detects the RLF of theaccess terminal. For example, the first cell may detect the RLF whiletrying to transmit the handover command and conclude that this is a caseof a too late handover from the first cell to the second cell. Asdiscussed herein, in some cases detection of RLF may involve detectingthe loss of lower layer synchronization with an access terminal duringan ongoing procedure of handing-over the access terminal from a firstcell (or access point) to a second cell (or access point). Thus, in someaspects, the detection of block 606 may comprise detecting RLF due totoo late handover, wherein the detection may comprise determining at afirst cell (or access point) that RLF occurred during handover of theaccess terminal from the first cell to a second cell (or access point).

As represented by block 608, the access terminal re-establishes theconnection at the second cell. As discussed herein, in conjunction withthe re-establishment of the connection, the second cell receives amessage from the access terminal that indicates that the access terminalexperienced RLF at the first cell.

As represented by block 610, the second cell sends an RLF report messagefor this access terminal to the first cell. As discussed above, thisreport message may be sent according to any suitable reporting scheme.The first cell receives this report message as represented by block 612.

As represented by block 614, the first cell detects too late handoverfailure based on the received RLF report message. For example, the firstcell may analyze the information in the report and conclude that thisrelates to the case of a too late handover from the first cell to thesecond cell. Thus, in some aspects, the detection of block 614 maycomprise detecting RLF due to too late handover. Here, the detection maycomprise receiving a message from a second cell (or access point) at afirst cell (or access point), wherein the message indicates that anaccess terminal re-establishing a connection at the second cellexperienced RLF at the first cell, and determining that the accessterminal was not handed-over to the second cell soon enough based on thereceived message. In addition, in some aspects, the determination thatthe access terminal was not handed-over to the second cell soon enoughmay comprise determining that the access terminal experienced the RLFduring handover of the access terminal from the first cell to a secondcell.

As represented by block 616, the first cell adapts one or more handoverparameters based on the detected too late handover failure. For example,the first cell may take the received information into consideration forthe purpose of optimization of handover parameters to avoid too latehandovers to the second cell in the future.

The flowcharts of FIGS. 7-9B describe operations that may be employed toprovide handover parameter adaptation based on detection of too earlyhandover. FIG. 7 relates to the first type of too early handover asdiscussed herein and FIGS. 8-9B relate to the second type of too earlyhandover as discussed herein.

Referring to FIG. 7, while connected to the first cell, handover of theaccess terminal to the second cell is commenced as represented by block702. In this example, the first cell successfully transmits a handovercommand to the access terminal requesting handover to the second cell.

As represented by block 704, the access terminal experiences RLF at thesecond cell while attempting to connect to the second cell. As discussedherein, the RLF may have occurred as a result of inadequateconfiguration of handover triggering parameters at the first cell (e.g.,first access point) that caused the handover from the first cell (e.g.,first access point) to the second cell (e.g., second access point) to betriggered too early for successful handover.

As represented by block 706, the access terminal re-establishes theconnection at the first cell. As discussed herein, in conjunction withthe re-establishment of the connection, the first cell receives amessage from the access terminal that indicates that the access terminalexperienced RLF at the second cell.

As represented by block 708, the first cell detects too early handoverfailure based on the connection re-establishment. For example, upondetecting connection re-establishment by the access terminal after anoutgoing handover attempt to another cell, the first cell may concludethat this is the case of a type 1 too early handover. Thus, in someaspects, the detection of block 708 may comprise detecting RLF due totoo early handover, wherein the detection may comprise determining at afirst cell (or access point) that an access terminal that re-establisheda connection at the first cell experienced RLF at a second cell (oraccess point) due to a prematurely initiated handover of the accessterminal from the first cell to the second cell.

As represented by block 710, the first cell adapts one or more handoverparameters based on the detection of too early handover failure. Forexample, the first cell may take the received information intoconsideration for the purpose of optimization of handover parameters toavoid too early handovers to the second cell in the future. As discussedherein, this may involve, for example, adapting (e.g., increasing) atleast one of: a time-to-trigger (TTT) parameter, an offset for a servingcell, a Cell Individual Offset (CIO), or a hysteresis parameter for anevent.

The adaptation of handover parameters as taught herein may take intoaccount one or more handover failure events. For example, a handoverparameter may be adapted for a specific cell based on detected too earlyhandovers associated with that cell and/or some other cell(s).Alternatively, a handover parameter may be adapted for a set of cellsbased on detected too early handovers failures associated with thosecells and/or some other cell(s).

Referring to the type 2 too early handover operations of FIG. 8, asrepresented by block 802, the access terminal is successfullyhanded-over from the first cell to the second cell. Here, the first cellcommences a timer upon being informed that the handover was completed(block 804). For example, the timer may be started once the first cellreceives a UE context release message from the second cell.

As represented by block 806, the access terminal experiences RLF at thesecond cell (e.g., as discussed herein). As represented by block 808,the access terminal re-establishes the connection at the first cell. Asdiscussed herein, in conjunction with the re-establishment of theconnection, the first cell receives a message from the access terminalthat indicates that the access terminal experienced RLF at the secondcell.

As represented by block 810, the first cell detects too early handoverfailure based on the connection re-establishment. For example, if theconnection re-establishment occurs before the timer expires, the firstcell may conclude that this is the case of a type 2 too early handover.Thus, in some aspects, the detection of block 810 may comprise detectingRLF due to too early handover, wherein the detection may comprisedetermining at a first cell (or access point) that an access terminalthat was handed-over from the first cell to a second cell (or accesspoint) re-established a connection at the first cell within a definedperiod of time after the first cell is informed that the handover wascompleted. As discussed herein, in some aspects, the defined period oftime may be configured based on a message received from a networkmanagement system.

As represented by block 812, the first cell may then adapt one or morehandover parameters based on the detection of too early handoverfailure. Various types of handover parameters may be adapted in thiscase. For example, at least one of: a time-to-trigger (TTT) parameter,an offset for a serving cell, a Cell Individual Offset (CIO), or ahysteresis parameter for an event, may be increased to reduce thelikelihood that too early handovers will occur in the future.

As discussed above, in some cases, the first cell may send an RLF reportmessage to the second cell as a result of the connectionre-establishment by the access terminal at the first cell, whereupon thesecond cell sends a handover report message back to the first cell.FIGS. 9A and 9B describe sample operations that may be performed in thiscase.

As represented by block 902, the access terminal is successfullyhanded-over from the first cell to the second cell. Here, the secondcell commences a timer upon completion of the handover (block 904). Asrepresented by block 906, the access terminal experiences RLF at thesecond cell (e.g., as discussed herein). As represented by block 908,the access terminal re-establishes the connection at the first cell asdiscussed herein. As represented by block 910, the first cell sends anRLF report message to the second cell. The second cell receives thismessage as represented by block 912.

As represented by block 914, if the second cell receives the RLF reportmessage (e.g., the connection re-establishment occurred) before thetimer expires, the second cell determines that this event relates to atype 2 too early handover for the first cell. Consequently, the secondcell sends a handover report message to the first cell at block 916, andthis message is received by the first cell at block 918. Thus, in someaspects, the handover report message may be sent as a result of adetermination that the RLF report message was received within a definedperiod of time after the access terminal was handed-over. As discussedherein, the defined period of time may commence upon sending of amessage (e.g., a UE context release message) requesting deletion of adata record pertaining to the access terminal in the first cell (e.g.,first access point). Also, the defined period of time may be configuredbased on a message received from a network management system. Asdiscussed herein, this message may comprise an indication of a type ofhandover failure associated with the RLF (e.g., a too early handoverindication). In addition, this message may comprise, for example, anidentifier of a cell at which the RLF occurred, an identifier of a cellat which the connection was re-established, and an identifier of theaccess terminal.

As represented by block 920, the first cell detects too late handoverfailure based on the received handover report message. Thus, in someaspects, the detection of block 920 may comprise detecting RLF due totoo early handover, wherein the detection may comprise receiving amessage from a second cell (or access point) at a first cell (or accesspoint), wherein the message indicates that RLF reported by the firstcell to the second cell was caused by the first cell handing the accessterminal over to the second cell too soon. As represented by block 922,the first cell adapts one or more handover parameters based on thedetection of too early handover failure.

The flowcharts of FIGS. 10-11B describe operations that may be employedto provide handover parameter adaptation based on detection of handoverto the wrong cell. FIG. 10 relates to the first type of handover to thewrong cell as discussed herein and FIGS. 11A-11B relate to the secondtype of handover to the wrong cell as discussed herein.

As represented by block 1002, while connected to the first cell,handover of the access terminal to the second cell is commenced. Forexample, the first cell may send a handover command message to theaccess terminal and store the access terminal context (UE context).

As represented by block 1004, the access terminal experiences RLF at thefirst cell during the handover procedure (e.g., while attempting toconnect to the second cell). As discussed herein, the RLF may haveoccurred as a result of inadequate configuration of handover triggeringparameters at the first cell (e.g., first access point) that causedhandover to the wrong cell.

As represented by block 1006, the access terminal re-establishes theconnection at a third cell. As discussed herein, in conjunction with there-establishment of the connection, the third cell receives a messagefrom the access terminal that indicates that the access terminalexperienced RLF at the second cell.

As represented by block 1008, the third cell sends an RLF report messageto the first cell, and this message is received by the first cell atblock 1010.

As represented by block 1012, the first cell detects type 1 handover tothe wrong cell based on the received RLF report message (e.g., based ona received indication of RLF). Here, the first cell may compare theidentifier of the target with the identifier of the cell (access point)from which the RLF report was received. If the identifier of the cell(access point) from which the RLF report was received is not identicalto the identifier of either the source or the target, then the firstcell may conclude that the handover was triggered towards a wrong cell.Thus, in some aspects, the detection of block 1012 may comprisedetermining at a first cell (or access point) that an access terminalthat re-established a connection at a second cell (or access point)experienced RLF at a third cell (or access point) due to a misdirectedhandover of the access terminal from the first cell to the third cell.

As represented by block 1014, the first cell may thus adapt one or morehandover parameters based on the detection of handover to the wrongcell. Various types of handover parameters may be adapted in this case.For example, a Cell Individual Offset (CIO) setting may be adapted toreduce the likelihood of handovers to the wrong cell in the future. Inaddition, other parameters such as a time-to-trigger (TTT) parameter, anoffset for a serving cell, or a hysteresis parameter for an event, maybe adapted here.

The adaptation of handover parameters as taught herein may take intoaccount one or more handover failure events. For example, a handoverparameter may be adapted for specified cell based on detected handoverto the wrong cell associated with the specified cell and/or some othercell(s). Alternatively, a handover parameter may be adapted for a set ofspecified cells based on detected handover to the wrong cell associatedwith those specified cells and/or some other cell(s).

Referring now to the type 2 handover to the wrong cell operations ofFIG. 11, as represented by block 1102, the access terminal issuccessfully handed-over from the first cell to the second cell. Here,the second cell sends a UE context release message for the accessterminal to the first cell and commences a timer (e.g., upon completionof the handover) as represented by block 1104. As represented by blocks1106 and 1108, the access terminal experiences RLF at the second celland re-establishes the connection at the third cell as discussed herein.As represented by block 1110, the third cell sends an RLF report messageto the second cell. The second cell receives this message as representedby block 1112.

As represented by block 1114, if the RLF report message is receivedbefore the timer expires, the second cell determines that this eventrelates to a type 2 handover to the wrong cell event for the first cell.For example, the second cell may compare the identifier of the sourcecell (access point) with the identifier of the cell (access point) fromwhich the RLF report was received. If the identifier of the cell fromwhich the RLF report was received is identical to the identifier of thesource cell, the second cell may elect to ignore the RLF report. On theother hand, if the identifier of the cell from which the RLF report wasreceived is not identical to the identifier of the source cell, thesecond cell sends a handover report message to the source cell (firstcell) at block 1116 (including a handover to wrong cell indication).This message is received by the first cell at block 1118. Thus, in someaspects, the handover report message may be sent as a result of adetermination that the RLF report message was received within a definedperiod of time after the access terminal was handed-over. As discussedherein, the defined period of time may commence upon sending of amessage (e.g., a UE context release message) requesting deletion of adata record pertaining to the access terminal in the first cell (e.g.,first access point). Also, the defined period of time may be configuredbased on a message received from a network management system. Asdiscussed herein, this message may comprise an indication of a type ofhandover failure associated with the RLF (e.g., a handover to a wrongcell indication). In addition, this message may comprise, for example,an identifier of a cell at which the RLF occurred, an identifier of acell at which the connection was re-established, an identifier of ahandover source cell, and an identifier of the access terminal.

As represented by block 1120, the first cell detects a handover to thewrong cell failure based on the received handover report message. Thus,in some aspects, the detection of block 1120 may be based on a handoverreport message received at a first cell (or access point) from a secondcell (or access point), wherein the handover message indicates that anaccess terminal that re-established a connection at a third cell (oraccess point) experienced RLF at the second cell during a handover ofthe access terminal from the first cell to the second cell. Asrepresented by block 1122, the first cell adapts one or more handoverparameters based on the detection of handover to the wrong cell.

FIGS. 12-13B describe techniques that may be employed to provideproactive handover parameter adaptation. In some aspects, proactivedetection is aimed at preventing future occurrences from happening basedon analysis of conditions prior to the occurrences.

As represented by blocks 1202 and 1204 of FIG. 12, a cell (an accesspoint) may determine (e.g., monitor) indications of signal quality(e.g., received signal strengths) of itself and of other surroundingcells as reported by any access terminals whose measurement reports werereceived by the cell. FIGS. 13A and 13B depict sample graphs of reportedquality indications Qn and Qs for a serving cell (line Mn) and a targetcell (line Ms), respectively. These quality indications may correspondto, for example, reference signal received quality (RSRQ), referencesignal received power (RSRP), or some other suitable quality metric.

The graphs illustrate certain parameters that may be used to determinewhen to trigger a measurement report. For example, the offset (e.g.,hysteresis) may indicate the amount by which the target qualityindication must exceed the serving cell indication before measurementreporting is triggered. In addition, time-to-trigger (TTT) may indicatethe minimum amount of time that the above condition must be continuouslymet before a measurement report is sent. In some cases, the indicationsof blocks 1202 and 1204 may be measured when a measurement report issent by an access terminal.

As represented by block 1206, the cell may identify a too late handoveror a too early handover (e.g., a too late or too early handoversignature) based on the determined indications of signal quality. Forexample, a signature of a likelihood of too late handovers may beidentified based on whether Qs is low and/or based on whether thedifference (Ds-n) between the quality indications when the measurementreport is sent by the access terminal is large as compared to the offset(e.g., the difference exceeds a defined offset by a defined amount).This condition is depicted in FIG. 13A. Conversely, a signature of alikelihood of too early handovers may be identified based on whether Qsis not low and/or based on whether the difference (Ds-n) between thequality indications when the measurement report is sent is small ascompared to the offset (e.g., the difference exceeds a defined offset byless than a defined amount). This condition is depicted in FIG. 13B.

As represented by block 1208, the cell may then adapt one or morehandover parameters, if applicable, to reduce the likelihood of too latehandovers or too early handovers in the future (e.g., proactivelymitigate too late or too early handovers). Thus, in some aspects, ahandover parameter may be adapted based on the indications determined atblocks 1202 and 1204 (e.g., based on a difference between theseindications, based on a too late or too early handover signature, etc.).These parameters (e.g., TTT, an offset for a serving cell, CIO, ahysteresis parameter, or some combination thereof) may be adapted, forexample, as discussed herein.

FIG. 14 describes operations that may be employed to provide handoverparameter adaptation based on detection of ping-ponging. Here,ping-ponging may be defined as successive avoidable handovers betweencells. In some aspects, the detection of ping-ponging may involve theexchange of access terminal-specific information between the cellsinvolved in the ping-ponging. This information may include, for example,the identities of the cells that the access terminal has recentlyvisited and the sojourn time for the access terminal in each visitedcell.

As represented by block 1402 of FIG. 14, the access terminal may thusmaintain visited cell history information. For example, for each visitedcell in a last visited cell list, the access terminal may maintain anidentifier (e.g., GCI) of the cell, an indication of the cell type, andan indication of the amount of time the access terminal stayed in thecell.

As represented by block 1404, the access terminal then provides thisinformation to a cell. For example, the access terminal may provide thisinformation to a cell in conjunction with handover of the cell. Thecells in the system may then share this information. For example, a cellmay send an information element (e.g., UE history information) in ahandover request message that includes the access terminal historyinformation.

As represented by block 1406, the cells may then detect ping-pongingbased on the history information. For example, each cell may examine thehistory information to determine whether the access terminal has beensuccessively handed-over between two cells, and whether the accessterminal has only stayed at each cell for relatively short periods oftime.

As represented by block 1408, if ping-ponging is detected, a cell mayadapt one or more of its handover parameters (e.g., TTT, an offset for aserving cell, CIO, a hysteresis parameter, or some combination thereof)in an attempt to prevent such ping-ponging in the future. For example,an incorrect setting of hysteresis may result in ping-ponging. Thus,upon detection of ping-ponging, a hysteresis parameter may be adapted inan attempt to reduce ping-ponging.

In some aspects, an operator (e.g., via an OAM) may configure parametersbased on network management policies and the operator's knowledge of thenetwork. For example, a network operator may configure a parameter basedon knowledge about levels and patterns of user mobility and theirfluctuations, desired trade-offs between handover performance andrequired network resources, and acceptable impact of handover parameterson load-balancing.

As discussed above, handover-related parameters may be autoconfigurableby the access point entities (e.g., self organizing network entities).In addition, in some implementations, a valid set of values (e.g., rangeof values, enumerated values, etc.) for these parameters may be providedto the access points (e.g., by an operator). In such a case, an accesspoint may select a value from within the configured set of values (e.g.,using handover parameter optimization algorithms as taught herein).

In addition, parameters used to detect handover failure may beconfigurable. For example, the timer values described above (e.g.,t_(early) _(—) _(HO) _(—) _(source), t_(early) _(—) _(HO) _(—)_(target), t_(store) _(—) _(UE) _(—) _(context)) may be configured by anoperator (e.g., via an OAM) and provided to the access points. In someimplementations, this may involve providing a valid set of values fromwhich the access points may select a desired value.

In some implementations, the OAM may configure a parameter to the samevalue for all access points (or cells) in a network or may configuredifferent values in different access points based on at least one of:their location, handover patterns, load, resource availability, vendor,or some other factor or factors.

FIG. 15 describes operations that may be employed to configureparameters for handover-related operations. These operations may beperformed, for example, by a network management system (e.g., an OAM)implemented at one or more network nodes or some other suitable location(e.g., in one or more access points). As represented by block 1502, anetwork management system configures one or more parameters fordetecting and/or mitigating handover failure. As discussed herein, sucha parameter may comprise, for example, a parameter for use by a cell todetermine whether an access terminal was handed-over too early, aparameter configured to mitigate too early handovers, a parameter (e.g.,a defined period of time) for use by a source cell to determine whetheran access terminal re-established a connection at the source cell withina defined period of time after the access terminal was handed-over to atarget cell, a parameter (e.g., a defined period of time) for use by atarget cell to determine whether an RLF report is received for an accessterminal within a defined period of time after the access terminal washanded-over to a target cell, a parameter for use by a cell to determinewhether an access terminal was handed-over to a wrong cell, a parameterconfigured to mitigate handovers to wrong cells, or a parameter (e.g., adefined period of time) for use by a target cell to determine whether anRLF report is received for an access terminal within a defined period oftime after the access terminal was handed-over to the target cell.

As represented by block 1504, the network management system sends theconfigured parameter(s) to one or more cells (or access points) in thenetwork. As represented by block 1506, each cell (or access point) mayconfigure one or more of these parameters (e.g., handover parameters).As represented by block 1508, each cell (or access point) may use one ormore of these parameters (e.g., timer values) to detect and/or mitigatehandover failure as taught herein.

FIG. 16 describes operations that may be employed in conjunction withincorrect handover (HO) parameter detection for intra-access pointhandover and inter-access point handover. In this example, an accesspoint exchanges messages with other access points via an X2-AP protocolmodule. In addition RRC messages are sent and received via an RRCmodule. In general, the illustrated operations are similar tocorresponding operations described herein. Of note, this exampleillustrates how an access point may concurrently detect different typesof handover-related failures and adapt handover parameters (via theprocess blocks).

FIG. 17 describes operations that may be employed in conjunction withincorrect handover parameter detection for inter-access point handover.In this example, an access point exchanges messages with other accesspoints via an X2-AP protocol module. In addition RRC messages arereceived via an RRC module. In general, the illustrated operations aresimilar to corresponding operations described herein. Of note, thisexample illustrates how an access point may concurrently detectdifferent types of handover-related failures and adapt handoverparameters (via the process blocks).

FIG. 18 illustrates several sample components that may be incorporatedinto nodes such as an access point 1802 (e.g., corresponding to theaccess points 104-108) and a network node 1804 (e.g., corresponding tothe network management system 118) to perform handover parameteradaptation operations as taught herein. The described components alsomay be incorporated into other nodes in a communication system. Forexample, other nodes in a system may include components similar to thosedescribed for the access point 1802 to provide similar functionality. Agiven node may contain one or more of the described components. Forexample, an access point may contain multiple transceiver componentsthat enable the access terminal to operate on multiple frequenciesand/or communicate via different technologies.

As shown in FIG. 18, the access point 1802 may include a transceiver1806 for communicating with other nodes. The transceiver 1806 includes atransmitter 1808 for sending signals (e.g., messages) and a receiver1810 for receiving signals (e.g., messages).

The access point 1802 and the network node 1804 also may include networkinterfaces 1812 and 1814, respectively, for communicating with oneanother or other network nodes. For example, the network interfaces 1812and 1814 may be configured to communicate with one or more network nodesvia a wired or wireless backhaul.

The access point 1802 and the network node 1804 also include othercomponents that may be used in conjunction with handover parameteradaptation operations as taught herein. For example, the access point1802 may include a handover failure detector 1816 for detecting handoverfailure-related conditions (e.g., RLF due to too late handover, RLF dueto too early handover, handover to a wrong cell, etc.) and for providingother related functionality as taught herein. The access point 1802 mayinclude a handover parameter adapter 1818 for adapting handover-relatedparameters and for providing other related functionality as taughtherein. The access point 1802 may include a parameter configurer 1820for configuring parameters (e.g., a defined period of time) and forproviding other related functionality as taught herein. The access point1802 may include a signal quality determiner 1822 for determining signalquality (e.g., an indication of signal quality, received signalstrength, etc.) and for providing other related functionality as taughtherein. In addition, the network node 1804 may include a communicationcontroller 1824 for sending parameters (e.g., via a message or someother suitable process) and for providing other related functionality astaught herein. Also, the network node 1804 may include a parameterconfigurer 1826 for configuring parameters (e.g., for detecting handoverfailure and/or for mitigating handover failure) and for providing otherrelated functionality as taught herein.

For convenience the access point 1802 and the network node 1804 areshown in FIG. 18 as including components that may be used in the variousexamples described herein. In practice, one or more of the illustratedcomponents may not be used in a given example. As an example, in someimplementations the access point 104 may not include the signal qualitydeterminer 1822.

Also, in some implementations the components of FIG. 18 may beimplemented in one or more processors (e.g., that uses and/orincorporates data memory for storing information or code used by theprocessor(s) to provide this functionality). For example, thefunctionality of blocks 1816-1822 may be implemented by a processor orprocessors of an access point and data memory of the access point. Inaddition, the functionality of blocks 1824 and 1826 may be implementedby a processor or processors of a network node and data memory of anetwork node.

In some aspects the teachings herein may be employed in a network thatincludes macro scale coverage (e.g., a large area cellular network suchas a 3G network, typically referred to as a macro cell network or a WAN)and smaller scale coverage (e.g., a residence-based or building-basednetwork environment, typically referred to as a LAN). As an accessterminal (AT) moves through such a network, the access terminal may beserved in certain locations by access points that provide macro coveragewhile the access terminal may be served at other locations by accesspoints that provide smaller scale coverage. In some aspects, the smallercoverage nodes may be used to provide incremental capacity growth,in-building coverage, and different services (e.g., for a more robustuser experience).

A node (e.g., an access point) that provides coverage over a relativelylarge area may be referred to as a macro node while a node that providescoverage over a relatively small area (e.g., a residence) may bereferred to as a femto node. It should be appreciated that the teachingsherein may be applicable to nodes associated with other types ofcoverage areas. For example, a pico node may provide coverage (e.g.,coverage within a commercial building) over an area that is smaller thana macro area and larger than a femto area. In various applications,other terminology may be used to reference a macro node, a femto node,or other access point-type nodes. For example, a macro node may beconfigured or referred to as an access node, base station, access point,eNodeB, macro cell, and so on. Also, a femto node may be configured orreferred to as a Home NodeB, Home eNodeB, access point base station,femto cell, and so on. In some implementations, a node may be associatedwith (e.g., divided into) one or more cells (e.g., sectors). A cellassociated with a macro node, a femto node, or a pico node may bereferred to as a macro cell, a femto cell, or a pico cell, respectively.

Access to a node may be restricted in some aspects. For example, a givenfemto node may only provide certain services to certain accessterminals. In deployments with so-called restricted (or closed) access,a given access terminal may only be served by the macro cell mobilenetwork and a defined set of femto nodes (e.g., the femto nodes thatreside within the corresponding user residence). In someimplementations, a node may be restricted to not provide, for at leastone node, at least one of: signaling, data access, registration, paging,or service.

In some aspects, a restricted femto node (which may also be referred toas a Closed Subscriber Group Home NodeB) is one that provides service toa restricted provisioned set of access terminals. This set may betemporarily or permanently extended as necessary. In some aspects, aClosed Subscriber Group (CSG) may be defined as the set of access points(e.g., femto nodes) that share a common access control list of accessterminals.

Various relationships may thus exist between a given femto node and agiven access terminal. For example, from the perspective of an accessterminal, an open femto node may refer to a femto node with unrestrictedaccess (e.g., the femto node allows access to any access terminal). Arestricted femto node may refer to a femto node that is restricted insome manner (e.g., restricted for access and/or registration). A homefemto node may refer to a femto node on which the access terminal isauthorized to access and operate on (e.g., permanent access is providedfor a defined set of one or more access terminals). A guest (or hybrid)femto node may refer to a femto node on which an access terminal istemporarily authorized to access or operate on. An alien femto node mayrefer to a femto node on which the access terminal is not authorized toaccess or operate on, except for perhaps emergency situations (e.g., 911calls).

From a restricted femto node perspective, a home access terminal mayrefer to an access terminal that is authorized to access the restrictedfemto node installed in the residence of that access terminal's owner(usually the home access terminal has permanent access to that femtonode). A guest access terminal may refer to an access terminal withtemporary access to the restricted femto node (e.g., limited based ondeadline, time of use, bytes, connection count, or some other criterionor criteria). An alien access terminal may refer to an access terminalthat does not have permission to access the restricted femto node,except for perhaps emergency situations, for example, such as 911 calls(e.g., an access terminal that does not have the credentials orpermission to register with the restricted femto node).

For convenience, the disclosure herein describes various functionalityin the context of a femto node. It should be appreciated, however, thata pico node may provide the same or similar functionality for a largercoverage area. For example, a pico node may be restricted, a home piconode may be defined for a given access terminal, and so on.

The teachings herein may be employed in a wireless multiple-accesscommunication system that simultaneously supports communication formultiple wireless access terminals. Here, each terminal may communicatewith one or more access points via transmissions on the forward andreverse links. The forward link (or downlink) refers to thecommunication link from the access points to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the access points. This communication link may beestablished via a single-in-single-out system, amultiple-in-multiple-out (MIMO) system, or some other type of system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system may provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system may support time division duplex (TDD) and frequencydivision duplex (FDD). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeam-forming gain on the forward link when multiple antennas areavailable at the access point.

FIG. 19 illustrates a wireless device 1910 (e.g., an access point) and awireless device 1950 (e.g., an access terminal) of a sample MIMO system1900. At the device 1910, traffic data for a number of data streams isprovided from a data source 1912 to a transmit (TX) data processor 1914.Each data stream may then be transmitted over a respective transmitantenna.

The TX data processor 1914 formats, codes, and interleaves the trafficdata for each data stream based on a particular coding scheme selectedfor that data stream to provide coded data. The coded data for each datastream may be multiplexed with pilot data using OFDM techniques. Thepilot data is typically a known data pattern that is processed in aknown manner and may be used at the receiver system to estimate thechannel response. The multiplexed pilot and coded data for each datastream is then modulated (i.e., symbol mapped) based on a particularmodulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for thatdata stream to provide modulation symbols. The data rate, coding, andmodulation for each data stream may be determined by instructionsperformed by a processor 1930. A data memory 1932 may store programcode, data, and other information used by the processor 1930 or othercomponents of the device 1910.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1920, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1920 then provides N_(T)modulation symbol streams to N_(T) transceivers (XCVR) 1922A through1922T. In some aspects, the TX MIMO processor 1920 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 1922 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 1922A through 1922T are thentransmitted from N_(T) antennas 1924A through 1924T, respectively.

At the device 1950, the transmitted modulated signals are received byN_(R) antennas 1952A through 1952R and the received signal from eachantenna 1952 is provided to a respective transceiver (XCVR) 1954Athrough 1954R. Each transceiver 1954 conditions (e.g., filters,amplifies, and downconverts) a respective received signal, digitizes theconditioned signal to provide samples, and further processes the samplesto provide a corresponding “received” symbol stream.

A receive (RX) data processor 1960 then receives and processes the N_(R)received symbol streams from N_(R) transceivers 1954 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 1960 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 1960 is complementary to that performed by the TX MIMOprocessor 1920 and the TX data processor 1914 at the device 1910.

A processor 1970 periodically determines which pre-coding matrix to use(discussed below). The processor 1970 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1972 may store program code, data, and other information used bythe processor 1970 or other components of the device 1950.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1938,which also receives traffic data for a number of data streams from adata source 1936, modulated by a modulator 1980, conditioned by thetransceivers 1954A through 1954R, and transmitted back to the device1910.

At the device 1910, the modulated signals from the device 1950 arereceived by the antennas 1924, conditioned by the transceivers 1922,demodulated by a demodulator (DEMOD) 1940, and processed by a RX dataprocessor 1942 to extract the reverse link message transmitted by thedevice 1950. The processor 1930 then determines which pre-coding matrixto use for determining the beam-forming weights then processes theextracted message.

FIG. 19 also illustrates that the communication components may includeone or more components that perform handover control operations astaught herein. For example, a handover control component 1990 maycooperate with the processor 1930 and/or other components of the device1910 to handover another device (e.g., device 1950) as taught herein.Similarly, a handover control component 1992 may cooperate with theprocessor 1970 and/or other components of the device 1950 to facilitatehanding-over of the device 1950. It should be appreciated that for eachdevice 1910 and 1950 the functionality of two or more of the describedcomponents may be provided by a single component. For example, a singleprocessing component may provide the functionality of the handovercontrol component 1990 and the processor 1930 and a single processingcomponent may provide the functionality of the handover controlcomponent 1992 and the processor 1970.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (CDMA) systems,Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-SpeedPacket Access (HSPA, HSPA+) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, or other multiple access techniques. Awireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and LowChip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). The teachingsherein may be implemented in a 3GPP Long Term Evolution (LTE) system, anUltra-Mobile Broadband (UMB) system, and other types of systems. LTE isa release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE aredescribed in documents from an organization named “3rd GenerationPartnership Project” (3GPP), while cdma2000 is described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). Although certain aspects of the disclosure may be describedusing 3GPP terminology, it is to be understood that the teachings hereinmay be applied to 3GPP (e.g., Re199, Re15, Re16, Re17) technology, aswell as 3GPP2 (e.g., 1xRTT, 1xEV-DO RelO, RevA, RevB) technology andother technologies.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). In someaspects, a node (e.g., a wireless node) implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

For example, an access terminal may comprise, be implemented as, orknown as user equipment, a subscriber station, a subscriber unit, amobile station, a mobile, a mobile node, a remote station, a remoteterminal, a user terminal, a user agent, a user device, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a session initiation protocol(SIP) phone, a wireless local loop (WLL) station, a personal digitalassistant (PDA), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smart phone), acomputer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music device, a video device, or a satellite radio), aglobal positioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

An access point may comprise, be implemented as, or known as a NodeB, aneNodeB, a radio network controller (RNC), a base station (BS), a radiobase station (RBS), a base station controller (BSC), a base transceiverstation (BTS), a transceiver function (TF), a radio transceiver, a radiorouter, a basic service set (BSS), an extended service set (ESS), amacro cell, a macro node, a Home eNB (HeNB), a femto cell, a femto node,a pico node, or some other similar terminology.

In some aspects a node (e.g., an access point) may comprise an accessnode for a communication system. Such an access node may provide, forexample, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link to the network. Accordingly, an access node mayenable another node (e.g., an access terminal) to access a network orsome other functionality. In addition, it should be appreciated that oneor both of the nodes may be portable or, in some cases, relativelynon-portable.

Also, it should be appreciated that a wireless node may be capable oftransmitting and/or receiving information in a non-wireless manner(e.g., via a wired connection). Thus, a receiver and a transmitter asdiscussed herein may include appropriate communication interfacecomponents (e.g., electrical or optical interface components) tocommunicate via a non-wireless medium.

A wireless node may communicate via one or more wireless communicationlinks that are based on or otherwise support any suitable wirelesscommunication technology. For example, in some aspects a wireless nodemay associate with a network. In some aspects the network may comprise alocal area network or a wide area network. A wireless device may supportor otherwise use one or more of a variety of wireless communicationtechnologies, protocols, or standards such as those discussed herein(e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, awireless node may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, awireless node may comprise a wireless transceiver with associatedtransmitter and receiver components that may include various components(e.g., signal generators and signal processors) that facilitatecommunication over a wireless medium.

The functionality described herein (e.g., with regard to one or more ofthe accompanying figures) may correspond in some aspects to similarlydesignated “means for” functionality in the appended claims. Referringto FIGS. 20-26, apparatuses 2000, 2100, 2200, 2300, 2400, 2500, and 2600are represented as a series of interrelated functional modules. Here, areceiving module 2002 may correspond at least in some aspects to, forexample, a receiver as discussed herein. A sending module 2004 maycorrespond at least in some aspects to, for example, a transmitter asdiscussed herein. A receiving module 2102 may correspond at least insome aspects to, for example, a receiver as discussed herein. A sendingmodule 2104 may correspond at least in some aspects to, for example, atransmitter as discussed herein. A configuring module 2106 maycorrespond at least in some aspects to, for example, a parameterconfigurer (e.g., parameter configurer 1820) as discussed herein. A toolate handover failure detecting module 2202 may correspond at least insome aspects to, for example, a handover failure detector as discussedherein. A handover parameter adapting module 2204 may correspond atleast in some aspects to, for example, a handover parameter adapter asdiscussed herein. A too early handover failure detecting module 2302 maycorrespond at least in some aspects to, for example, a handover failuredetector as discussed herein. A handover parameter adapting module 2304may correspond at least in some aspects to, for example, a handoverparameter adapter as discussed herein. A configuring module 2306 maycorrespond at least in some aspects to, for example, a parameterconfigurer (e.g., parameter configurer 1820) as discussed herein. Ahandover to wrong cell detecting module 2402 may correspond at least insome aspects to, for example, a handover failure detector as discussedherein. A handover parameter adapting module 2404 may correspond atleast in some aspects to, for example, a handover parameter adapter asdiscussed herein. An indication of signal quality determining module2502 may correspond at least in some aspects to, for example, a signalquality determiner detector as discussed herein. A handover parameteradapting module 2504 may correspond at least in some aspects to, forexample, a handover parameter adapter as discussed herein. A parameterconfiguring module 2602 may correspond at least in some aspects to, forexample, a parameter configurer (e.g., parameter configurer 1824) asdiscussed herein. A parameter sending module 2604 may correspond atleast in some aspects to, for example, a communication controller asdiscussed herein.

The functionality of the modules of FIGS. 20-26 may be implemented invarious ways consistent with the teachings herein. In some aspects thefunctionality of these modules may be implemented as one or moreelectrical components. In some aspects the functionality of these blocksmay be implemented as a processing system including one or moreprocessor components. In some aspects the functionality of these modulesmay be implemented using, for example, at least a portion of one or moreintegrated circuits (e.g., an ASIC). As discussed herein, an integratedcircuit may include a processor, software, other related components, orsome combination thereof. The functionality of these modules also may beimplemented in some other manner as taught herein. In some aspects oneor more of any dashed blocks in FIGS. 20-26 are optional.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements. In addition, terminologyof the form “at least one of: A, B, or C” used in the description or theclaims means “A or B or C or any combination of these elements.”

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (IC), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media. It should beappreciated that a computer-readable medium may be implemented in anysuitable computer-program product.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method of communication, comprising: detecting at least one radio link failure due to too late handover; and adapting at least one handover parameter at a first cell based on the detection, wherein the detection comprises: receiving a message from a second cell at the first cell, wherein the message indicates that an access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell; and determining at the first cell, after the radio link failure of the access terminal at the first cell, that the access terminal was not handed-over to the second cell soon enough based on the received message from the second cell indicating that the access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell, the first cell being a source cell and the second cell being a target cell.
 2. The method of claim 1, wherein the detection comprises determining at the first cell that a radio link failure occurred during a handover of an access terminal from the first cell to the second cell.
 3. The method of claim 2, wherein the determination that the radio link failure occurred comprises detecting loss of lower layer synchronization with the access terminal during an ongoing procedure of handing-over the access terminal from the first cell to the second cell.
 4. The method of claim 1, wherein the determination that the access terminal was not handed-over to the second cell soon enough comprises determining that the access terminal experienced the radio link failure during handover from the first cell to the second cell.
 5. The method of claim 1, wherein the at least one handover parameter comprises at least one of the group consisting of: a time-to-trigger parameter, an offset for a serving cell, a Cell Individual Offset, and a hysteresis parameter for an event.
 6. The method of claim 1, wherein the adaption of the at least one handover parameter comprises at least one of the group consisting of: reducing a time-to-trigger parameter, reducing an offset for a serving cell, reducing a Cell Individual Offset, and reducing a hysteresis parameter for an event.
 7. The method of claim 1, wherein the message is a radio link failure (RLF) indication message.
 8. An apparatus for communication, comprising: a handover failure detector configured to detect at least one radio link failure due to too late handover; and a handover parameter adapter configured to adapt at least one handover parameter at a first cell based on the detection, wherein the detection comprises: receiving a message from a second cell at the first cell, wherein the message indicates that an access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell; and determining at the first cell, after the radio link failure of the access terminal at the first cell, that the access terminal was not handed-over to the second cell soon enough based on the received message from the second cell indicating that the access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell, the first cell being a source cell and the second cell being a target cell.
 9. The apparatus of claim 8, wherein the detection comprises determining at the first cell that a radio link failure occurred during a handover of an access terminal from the first cell to the second cell.
 10. The apparatus of claim 8, wherein the determination that the access terminal was not handed-over to the second cell soon enough comprises determining that the access terminal experienced the radio link failure during handover from the first cell to the second cell.
 11. An apparatus for communication, comprising: means for detecting at least one radio link failure due to too late handover; and means for adapting at least one handover parameter at a first cell based on the detection, wherein the detection comprises: receiving a message from a second cell at the first cell, wherein the message indicates that an access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell; and determining at the first cell, after the radio link failure of the access terminal at the first cell, that the access terminal was not handed-over to the second cell soon enough based on the received message from the second cell indicating that the access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell, the first cell being a source cell and the second cell being a target cell.
 12. The apparatus of claim 11, wherein the detection comprises determining at the first cell that a radio link failure occurred during a handover of an access terminal from the first cell to the second cell.
 13. The apparatus of claim 11, wherein the determination that the access terminal was not handed-over to the second cell soon enough comprises determining that the access terminal experienced the radio link failure during handover from the first cell to the second cell.
 14. A non-transitory computer-readable medium comprising code for causing a computer to: detect at least one radio link failure due to too late handover; and adapt at least one handover parameter at a first cell based on the detection, wherein the detection comprises: receiving a message from a second cell at the first cell, wherein the message indicates that an access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell; and determining at the first cell, after the radio link failure of the access terminal at the first cell, that the access terminal was not handed-over to the second cell soon enough based on the received message from the second cell indicating that the access terminal re-establishing a connection at the second cell experienced radio link failure at the first cell, the first cell being a source cell and the second cell being a target cell.
 15. The non-transitory computer-readable medium of claim 14, wherein the detection comprises determining at the first cell that a radio link failure occurred during a handover of an access terminal from the first cell to the second cell.
 16. The non-transitory computer-readable medium of claim 14, wherein the determination that the access terminal was not handed-over to the second cell soon enough comprises determining that the access terminal experienced the radio link failure during handover from the first cell to the second cell.
 17. A method of communication, comprising: detecting at least one radio link failure due to too early handover; and adapting at least one handover parameter at a first cell based on the detection, wherein the detection comprises receiving a handover report message reporting on a previous handover from a second cell at the first cell, the first cell being a source cell and the second cell being a target cell, wherein the message received at the first cell from the second cell indicates that a radio link failure reported by the first cell to the second cell was caused by the first cell handing an access terminal over to the second cell too soon.
 18. The method of claim 17, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the first cell experienced radio link failure at the second cell due to a prematurely initiated handover of the access terminal from the first cell to the second cell.
 19. The method of claim 17, wherein the detection comprises determining at the first cell that an access terminal that was handed-over from the first cell to the second cell re-established a connection at the first cell within a defined period of time after the first cell is informed that the handover was completed.
 20. The method of claim 19, wherein the first cell is informed that the handover was completed via receipt of a user equipment context release message from the second cell.
 21. The method of claim 19, further comprising configuring the defined period of time based on a message received from a network management system.
 22. The method of claim 17, wherein the at least one handover parameter comprises at least one of the group consisting of: a time-to-trigger parameter, an offset for a serving cell, a Cell Individual Offset, and a hysteresis parameter for an event.
 23. The method of claim 17, wherein the adaption of the at least one handover parameter comprises at least one of the group consisting of: increasing a time-to-trigger parameter, increasing an offset for a serving cell, increasing a Cell Individual Offset, and increasing a hysteresis parameter for an event.
 24. An apparatus for communication, comprising: a handover failure detector configured to detect at least one radio link failure due to too early handover; and a handover parameter adapter configured to adapt at least one handover parameter at a first cell based on the detection, wherein the detection comprises receiving a handover report message reporting on a previous handover from a second cell at the first cell, the first cell being a source cell and the second cell being a target cell, wherein the message received at the first cell from the second cell indicates that a radio link failure reported by the first cell to the second cell was caused by the first cell handing an access terminal over to the second cell too soon.
 25. The apparatus of claim 24, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the first cell experienced radio link failure at the second cell due to a prematurely initiated handover of the access terminal from the first cell to the second cell.
 26. The apparatus of claim 24, wherein the detection comprises determining at the first cell that an access terminal that was handed-over from the first cell to the second cell re-established a connection at the first cell within a defined period of time after the first cell is informed that the handover was completed.
 27. An apparatus for communication, comprising: means for detecting at least one radio link failure due to too early handover; and means for adapting at least one handover parameter at a first cell based on the detection, wherein the detection comprises receiving a handover report message reporting on a previous handover from a second cell at the first cell, the first cell being a source cell and the second cell being a target cell, wherein the message received at the first cell from the second cell indicates that a radio link failure reported by the first cell to the second cell was caused by the first cell handing an access terminal over to the second cell too soon.
 28. The apparatus of claim 27, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the first cell experienced radio link failure at the second cell due to a prematurely initiated handover of the access terminal from the first cell to the second cell.
 29. The apparatus of claim 27, wherein the detection comprises determining at the first cell that an access terminal that was handed-over from the first cell to the second cell re-established a connection at the first cell within a defined period of time after the first cell is informed that the handover was completed.
 30. A non-transitory computer-readable medium comprising code for causing a computer to: detect at least one radio link failure due to too early handover; and adapt at least one handover parameter at a first cell based on the detection, wherein the detection comprises receiving a handover report message reporting on a previous handover from a second cell at the first cell, the first cell being a source cell and the second cell being a target cell, wherein the message received at the first cell from the second cell indicates that a radio link failure reported by the first cell to the second cell was caused by the first cell handing an access terminal over to the second cell too soon.
 31. The non-transitory computer-readable medium of claim 30, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the first cell experienced radio link failure at the second cell due to a prematurely initiated handover of the access terminal from the first cell to the second cell.
 32. The non-transitory computer-readable medium of claim 30, wherein the detection comprises determining at the first cell that an access terminal that was handed-over from the first cell to the second cell re-established a connection at the first cell within a defined period of time after the first cell is informed that the handover was completed.
 33. A method of communication, comprising: detecting at least one handover to a wrong cell; and adapting at least one handover parameter at a first cell based on the detection, wherein the detection is based on a handover report message reporting on a previous handover received at the first cell from a second cell, the first cell being a source cell and the second cell being a target cell and the wrong cell, wherein the handover report message received at the first cell from the second cell indicates that an access terminal that re-established a connection at a third cell experienced radio link failure at the second cell during a handover of the access terminal from the first cell to the second cell.
 34. The method of claim 33, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the third cell experienced radio link failure at the second cell due to a misdirected handover of the access terminal from the first cell to the second cell.
 35. The method of claim 34, wherein the detection is based on an indication of the radio link failure received from the third cell.
 36. The method of claim 33, wherein the at least one handover parameter comprises at least one of the group consisting of: a time-to-trigger parameter, an offset for a serving cell, a Cell Individual Offset, and a hysteresis parameter for an event.
 37. An apparatus for communication, comprising: a handover failure detector configured to detect at least one handover to a wrong cell; and a handover parameter configured to adapt at least one handover parameter at a first cell based on the detection, wherein the detection is based on a handover report message reporting on a previous handover received at the first cell from a second cell, the first cell being a source cell and the second cell being a target cell and the wrong cell, wherein the handover report message received at the first cell from the second cell indicates that an access terminal that re-established a connection at a third cell experienced radio link failure at the second cell during a handover of the access terminal from the first cell to the second cell.
 38. The apparatus of claim 37, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the third cell experienced radio link failure at the second cell due to a misdirected handover of the access terminal from the first cell to the second cell.
 39. An apparatus for communication, comprising: means for detecting at least one handover to a wrong cell; and means for adapting at least one handover parameter at a first cell based on the detection, wherein the detection is based on a handover report message reporting on a previous handover received at the first cell from a second cell, the first cell being a source cell and the second cell being a target cell and the wrong cell, wherein the handover report message received at the first cell from the second cell indicates that an access terminal that re-established a connection at a third cell experienced radio link failure at the second cell during a handover of the access terminal from the first cell to the second cell.
 40. The apparatus of claim 39, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the third cell experienced radio link failure at the second cell due to a misdirected handover of the access terminal from the first cell to the second cell.
 41. A non-transitory computer-readable medium comprising code for causing a computer to: detect at least one handover to a wrong cell; and adapt at least one handover parameter at a first cell based on the detection, wherein the detection is based on a handover report message reporting on a previous handover received at the first cell from a second cell, the first cell being a source cell and the second cell being a target cell and the wrong cell, wherein the handover report message received at the first cell from the second cell indicates that an access terminal that re-established a connection at a third cell experienced radio link failure at the second cell during a handover of the access terminal from the first cell to the second cell.
 42. The non-transitory computer-readable medium of claim 41, wherein the detection comprises determining at the first cell that an access terminal that re-established a connection at the third cell experienced radio link failure at the second cell due to a misdirected handover of the access terminal from the first cell to the second cell.
 43. A method of communication of a first cell, comprising: determining at least one first indication of signal quality associated with the first cell and at least one second indication of signal quality associated with a second cell; identifying one of a too late handover signature or a too early handover signature based on a difference between the at least one first indication of signal quality and the at least one second indication of signal quality; and adapting at least one handover parameter at the first cell based on the at least one first indication and the at least one second indication, the first cell being a source cell and the second cell being a target cell, wherein the adaption is further based on whether a too late handover signature or a too early handover signature is identified by the first cell.
 44. The method of claim 43, wherein the at least one first indication and the at least one second indication are determined based on when a measurement report is sent by an access terminal.
 45. The method of claim 43, wherein the adaption comprises: identifying the too late handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too late handovers.
 46. The method of claim 43, wherein the adaption comprises: identifying the too early handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by less than a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too early handovers.
 47. The method of claim 43, wherein the at least one first indication and the at least one second indication comprise indications of received signal strength.
 48. The method of claim 43, wherein the at least one handover parameter comprises at least one of the group consisting of: a time-to-trigger parameter, an offset for a serving cell, a Cell Individual Offset, and a hysteresis parameter for an event.
 49. The method of claim 43, wherein the adaption is further based on an amount by which the difference exceeds a defined offset.
 50. An apparatus for communication, the apparatus being a first cell, comprising: a signal quality determiner configured to determine at least one first indication of signal quality associated with the first cell and at least one second indication of signal quality associated with a second cell; and a handover parameter adapter configured to identify one of a too late handover signature or a too early handover signature based on a difference between the at least one first indication of signal quality and the at least one second indication of signal quality, and to adapt at least one handover parameter at the first cell based on the at least one first indication and the at least one second indication, the first cell being a source cell and the second cell being a target cell, wherein the adaption is further based on whether a too late handover signature or a too early handover signature is identified by the first cell.
 51. The apparatus of claim 50, wherein the adaption comprises: identifying the too late handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too late handovers.
 52. The apparatus of claim 50, wherein the adaption comprises: identifying the too early handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by less than a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too early handovers.
 53. An apparatus for communication, the apparatus being a first cell, comprising: means for determining at least one first indication of signal quality associated with the first cell and at least one second indication of signal quality associated with a second cell; means for identifying one of a too late handover signature or a too early handover signature based on a difference between the at least one first indication of signal quality and the at least one second indication of signal quality; and means for adapting at least one handover parameter at the first cell based on the at least one first indication and the at least one second indication, the first cell being a source cell and the second cell being a target cell, wherein the adaption is further based on whether a too late handover signature or a too early handover signature is identified by the first cell.
 54. The apparatus of claim 53, wherein the adaption comprises: identifying the too late handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too late handovers.
 55. The apparatus of claim 53, wherein the adaption comprises: identifying the too early handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by less than a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too early handovers.
 56. A non-transitory computer-readable medium comprising code for causing a computer to: determine at least one first indication of signal quality associated with the first cell and at least one second indication of signal quality associated with a second cell; identify one of a too late handover signature or a too early handover signature based on a difference between the at least one first indication of signal quality and the at least one second indication of signal quality; and adapt at least one handover parameter at the first cell based on the at least one first indication and the at least one second indication, the first cell being a source cell and the second cell being a target cell, wherein the adaption is further based on whether a too late handover signature or a too early handover signature is identified by the first cell.
 57. The non-transitory computer-readable medium of claim 56, wherein the adaption comprises: identifying the too late handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too late handovers.
 58. The non-transitory computer-readable medium of claim 56, wherein the adaption comprises: identifying the too early handover signature based on whether the difference between the at least one first indication and the at least one second indication exceeds a defined offset by less than a defined amount; and adapting the at least one handover parameter based on the identified signature to proactively mitigate too early handovers. 